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Biochemistry > Genetics of Development > Flashcards

Genetics of Development Flashcards

1
Q

Robin sequence

A

A case of cleft palate in which an extrinsic constraint on fetus interferes with growth of jaw; also causes sleep apnea due to airway constriction

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2
Q

Treacher-Collins syndrome

A

A cause of cleft palate; autosomal dominant disorder that causes small jaw, down-slanting palpebral fissures, and malar hypoplasia; recurrent risk is 50%

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3
Q

Embryonal period of development

A

Weeks 1-8: 4 cell divisions without cell growth –> morula –> blastocyst –> epiblast and hypoblast differentiation –> gastrulation and three germ layers (endoderm, ectoderm, and mesoderm) –> primitive streak –> first axis

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4
Q

Morula

A

16 cell embryo that transforms into blastocyst

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5
Q

Blastocyst

A

Comes from morula; hollow sphere containing a group of cells called inner cell mass

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6
Q

Time of implantation

A

Day 7-12

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7
Q

Inner cell mass

A

Group of cells inside blastocyst; forms epiblast during time of implantation

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8
Q

Epiblast

A

Formed from inner cell mass; forms embryo

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9
Q

Gastrulation

A

Formation of three germ layers (endoderm, ectoderm, and mesoderm); produces primitive streak

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10
Q

Endoderm

A

Forms cells of gut and lung epithelium

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11
Q

Mesoderm

A

Forms bone, muscle, and most internal organs

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12
Q

Ectoderm

A

Forms skin and nervous system

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13
Q

Regulative vs. mosaic development

A
  1. Regulative phase is the first phase, where cells are functionally equivalent and loss can be compensated for – phase where identical twins start and where chromosomal aberrations need to be looked for
  2. Mosaic phase is the second phase, where it is important for cells NOT to be lost because they cannot be compensated for – leads to loss of tissue
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14
Q

Pre-implantation diagnosis

A

Removing cell from embryo in morula phase (of regulative phase) to check for chromosomal aberrations

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15
Q

Primitive streak

A

Formed from ectodermal cells invading to form mesoderm; takes place after about 14 days of gestation; marks groove at which ectodermal cells invade space between epiblast and hypoblast to form separate germ layer

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16
Q

What are the three axes in the developing embryo?

A
  1. Anterior/posterior
  2. Dorsal/ventral
  3. Left-right
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17
Q

Which is the first visible axis in developing embryo?

A

Anterior/posterior axis

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18
Q

Anterior/posterior axis

A

First visible structure in embryo; defined by primitive streak which is defined by position of sperm entry into egg; node exists at anterior end of primitive streak

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19
Q

Function of the node

A

Forms anterior end of primitive streak and gives off noggin and chordin

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20
Q

Nodal

A

Gene that is required for formation of primitive streak (also for formation of left/right axis); diffuses through tissues and goes wherever needed

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21
Q

Noggin and chordin

A

Secreted protein used to specify dorsal/ventral axis; induces dorsal development in concentration-dependent manner; secreted from the node

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22
Q

Sonic hedgehog (Shh)

A

Important morphogen secreted from the notochord that causes left/right asymmetry due to its asymmetric expression; causes nodal to be expressed more on left side to initiate left-looping of heart tube

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23
Q

Situs solitus

A

Normal left/right axis formation (asymmetry of thoracic cavity)

24
Q

Situs inversus

A

Defect in left/right axis formation in which all organs are complete mirror image of normal

25
Q

Situs ambiguus

A

Defect in left/right axis formation in which all organs have randomized orientation; usually accompanied by heart defects

26
Q

3 axes of the developing limb

A
  1. Proximal-distal = shoulder to fingertip
  2. Anterior-posterior = thumb to fifth finger
  3. Dorsal-ventral = dorsum to palm
27
Q

Homeobox (HOX) genes

A

Family of transcription factors containing the homeodomain; 4 clusters on 4 genes with 13 members

28
Q

Homeodomain

A

Special DNA binding domain used by HOX genes

29
Q

Patterning and the role of HOX

A

Determined by HOX genes; expression of each gene correlates with position of respective cell in embryo and timing (earliest HOX genes expressed near head, latest near caudal end)

30
Q

5 processes in which cells participate in development

A
  1. Gene regulation
  2. Cell-cell signaling
  3. Development of cell shape/polarity
  4. Movement and migration of cells
  5. Programmed cell death
31
Q

Clinical dysmorphology

A

Field of study describing etiology of birth defects that gives valuable clues to underlying abnormalities

32
Q

Terms to describe defects

A

Cause of abnormality = malformation, deformation, and disruption
How phenotypes are seen = syndrome and sequence

33
Q

Malformation

A

Results from intrinsic abnormality in developmental process (ex. polydactyly due to interference with limb development)

34
Q

Polydactyly

A

Too many fingers on one hand

35
Q

Deformation

A

Results from extrinsic (outside of developing embryo, normally from environment in womb) influence on development (ex. lack of amniotic fluid, or oligohydramnios)

36
Q

Disruption

A

Results from destruction of developing tissue (ex. amputations by strings of amniotic tissue)

37
Q

Isolated anomalies

A

Defects affecting a single body region (ex. cleft palate) that are sporadic or multifactorial in origin; account for about 60% of major birth defects

38
Q

Sequences

A

Caused by single defect starting a cascade of events (ex. Robin sequence); usually sporadic or multifactorial; requires more preventative management and has higher risk for complications

39
Q

Syndromes

A

Caused by single defect that simultaneously affects development of different tissues (ex. Down syndrome); requires more preventative management and has higher risk for complications

40
Q

Impact of problems during first 4 weeks

A

Occur during blastogenesis; produce multiple major abnormalities in entire embryonic regions (ex. VACTERL association)

41
Q

VACTERL association

A

Vertebral defects, Anal atresia, Cardiac abnormalities, Tracheo-Esophageal fistula, Renal and Limb abnormalities; originate from damage to developing mesoderm at 20-25 days from conception (maternal diabetes is risk factor)

42
Q

Impact of problems during weeks 5-8

A

Occur during organogenesis; produce abnormalities in specific organs and single major anomalies (ex. congenital heart defects)

43
Q

Impact of problems later in development (after week 9)

A

Occur after organ formation; mild effect such as palmar crease

44
Q

Major anomalies

A

Anomalies with surgical or cosmetic consequences (ex. cleft lip or amputated limb)

45
Q

Minor anomalies

A

Anomalies with little impact on well-being on the patient that give diagnostic clues about presence of a syndrome

46
Q

Percentage of total mortality of birth defects

A

20% (most common cause of death in infants)

47
Q

Percentage of infant deaths due to prematurity

A

20%

48
Q

Percentage of children born with recognizable birth defects

A

2-3%

49
Q

5 most frequent birth defects

A
  1. Heart defects (1/100-200)
  2. Pyloric stenosis (1/300)
  3. Neural tube defects (1/1,000)
  4. Orofacial clefts (1/700-1,000)
  5. Clubfoot (1/1,000)
50
Q

Percentage of birth defects with complex inheritance

A

50%

51
Q

Percentage of birth defects caused by chromosomal defects

A

25%

52
Q

Percentage of birth defects caused by single-gene mutations

A

20%

53
Q

Percentage of cases that can be traced to non-genetic factors (maternal medication/infections)

A

5%

54
Q

Segmental overgrowth

A

Can be caused by one additional cell division per affected cell late in development; typically fatal in early development

55
Q

Robustness of development

A

Many factors that are capable to disturb orderly development are recognized by developing embryo and countered through regulatory mechanisms

56
Q

Role of chance in expression of developmental defects

A

Formin mutation does not cause but instead increases the probability for developing renal aplasia

Biochemistry (14 decks)

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